Fuel source for electrochemical cell

ABSTRACT

A fuel source for an electrochemical cell includes two or more chemical hydride pellets, a flexible, porous, liquid water impermeable, hydrogen and water vapor permeable membrane in contact with and at least partially surrounding each hydride pellet, and a porous metal hydride layer positioned between each hydride pellet. Air gaps are between each pellet.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication 61/144,911 filed Jan. 15, 2009, entitled “FUEL SOURCE FORELECTROCHEMICAL CELL,” the contents of which applications areincorporated herein by reference in their entirety.

BACKGROUND

1. Field of Invention

This invention relates to fuel sources for electrochemical cells such ashydrogen fuel cells.

2. Background

Hydrogen fuel cells have been proposed utilizing a reactive chemicalhydride as a fuel source. Normally the chemical hydride is reacted withwater to liberate hydrogen gas, which then is consumed by the fuel cell.Other protonic solvents besides water (e.g. alcohols, organic acids) mayalso be employed.

In such a fuel cell system, a housing is often employed to contain thefuel and reaction products in order to protect the fuel from reactingwith atmospheric moisture when the fuel cell is not in service and tocollect the generated hydrogen so it can be conducted to the fuel cell.It is desirable to include a maximum quantity of fuel in a housing of agiven volume in order to achieve the highest possible hydrogen outputand the longest possible running time for the fuel cell. However, thedisadvantage of packing fuel too tightly into the housing is that theaccess of water to some parts of the fuel becomes restricted and therate of hydrogen generation is then limited by the slow diffusion ofwater into the bulk of the fuel. As solid reaction products accumulate,they may further restrict water access, choking off the reaction.Ultimately, the reaction may reach a standstill and fuel utilizationwill be incomplete.

SUMMARY

Embodiments of the invention relate to a fuel source for anelectrochemical cell. The fuel source comprises two or more chemicalhydride pellets, a flexible, porous, liquid water impermeable,water-vapor and hydrogen permeable membrane in contact with and at leastpartially surrounding each chemical hydride pellet and a porous metalhydride layer positioned between each chemical hydride pellet. Air gapsare between each pellet.

Embodiments also relate to a fuel source for an electrochemical cell,including two or more chemical hydride pellets, positioned in two ormore stacks, a flexible, porous, liquid water impermeable, water-vaporand hydrogen permeable membrane in contact with and at least partiallysurrounding each hydride pellet, a porous metal hydride layer,separating each hydride pellet stack and one or more spacers, positionedbetween each pellet. Air gaps are between each pellet.

Embodiments further relate to a fuel source for an electrochemical cell,including two or more chemical hydride pellets, positioned in a stack, aflexible, porous, liquid water impermeable, hydrogen and water vaporpermeable membrane, in contact with and at least partially surroundingeach chemical hydride pellet; a porous metal hydride pellet, positionedadjacent to one end of the stack and one or more spacers, positionedbetween each chemical hydride pellet and between the chemical hydridepellet and the porous metal hydride layer. Air gaps are between eachpellet.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsdescribe substantially similar components throughout the several views.Like numerals having different letter suffixes represent differentinstances of substantially similar components. The drawings illustrategenerally, by way of example, but not by way of limitation, variousembodiments discussed in the present document.

FIG. 1 illustrates a cross-sectional view of a fuel source, according tosome embodiments.

FIG. 2 illustrates a cross-sectional view of an alternative fuel sourceconfiguration, according to some embodiments.

FIG. 3 illustrates a cross-sectional view of an alternative fuel sourceconfiguration, according to some embodiments.

DETAILED DESCRIPTION

The following detailed description includes references to theaccompanying drawings, which form a part of the detailed description.The drawings show, by way of illustration, specific embodiments in whichthe invention may be practiced. These embodiments, which are alsoreferred to herein as “examples,” are described in enough detail toenable those skilled in the art to practice the invention. Theembodiments may be combined, other embodiments may be utilized, orstructural, and logical changes may be made without departing from thescope of the present invention. The following detailed description is,therefore, not to be taken in a limiting sense, and the scope of thepresent invention is defined by the appended claims and theirequivalents.

In this document, the terms “a” or “an” are used to include one or morethan one and the term “or” is used to refer to a nonexclusive “or”unless otherwise indicated. In addition, it is to be understood that thephraseology or terminology employed herein, and not otherwise defined,is for the purpose of description only and not of limitation.Furthermore, all publications, patents, and patent documents referred toin this document are incorporated by reference herein in their entirety,as though individually incorporated by reference. In the event ofinconsistent usages between this document and those documents soincorporated by reference, the usage in the incorporated referenceshould be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

Embodiments of the invention relate principally to a fuel source for anelectrochemical cell, such as a fuel cell. However, such a fuel sourcemay also be employed for other purposes such as supplying fuel to acombustion engine, to a heating device, to a cooling device (e.g. adevice operating with a Kelvinator type of refrigeration cycle), to aflame employed for lighting, to a flame employed as part of ananalytical instrument, to a flame employed in a cutting or welding torchand for other devices which consume a fuel either via a flame or bycatalytic oxidation to produce a useful effect. Embodiments of thepresent invention provide an improved fuel source, such as a pellet,which allows higher average rates of hydrogen generation (power) andincreased extracted energy by providing a controlled porosity fuelstructure, including channels, to maintain a low gas diffusionresistance throughout the discharging process.

Referring to FIG. 1, a cross-sectional view 100 of a fuel source isshown, according to some embodiments. Two or more compressed porouschemical hydride pellets 104 may be contacted with, or at leastpartially surrounded or wrapped with a flexible, porous water-vaporpermeable layer 108 (such as TEFLON, GORE TEX, or NAFION) that preventsfuel particles from expanding into gas diffusion channels 106, adjacentthe pellets 104 or other fuel source pellets. The gas diffusion channelsmay be constructed of porous metal hydride pellets for example. Air gaps102 are between individual chemical hydride pellets 104, and between thechemical hydride pellets 104 and perforated enclosure 112. A liquidwater impermeable, hydrogen and water-vapor permeable membrane or aparticulate membrane 110 (such as TEFLON, GORE TEX, or NAFION) may alsobe positioned between chemical hydride pellets 104 and enclosure 112.

The chemical hydride is any water-reactive hydrogen-producing materialthat reacts with water vapor to produce hydrogen. Exemplary chemicalhydrides comprise LiAlH₄, NaAlH₄, KAlH₄, MgAlH₄, CaH₂, LiBH₄, NaBH₄,LiH, and MgH₂, alkali metals, alkaline earth metals, and alkali metalsalicides. Specific chemical hydrides comprise LiAlH₄, NaAlH₄, NaBH₄,LiBH₄, LiH, or any combination thereof. The chemical hydride pellets 104may be manufactured with a controlled porosity. The perforated enclosure112 may be the same container as the housing or the enclosure 112 may bea separate structure that is located inside the housing. The enclosure112 may contain perforations to permit water ingress through theenclosure 112 walls into the outer surface of the pellet, from wherewater can then diffuse inward. The enclosure 112 may be shaped as acylinder or other shapes may be utilized. Such shapes include, forexample, a disc, cube, prism, or sphere.

The size of the particles that comprise the chemical hydride pelletsshould be in a range from 1-10 μm diameter to minimize resistance to theflow of water vapor through the chemical hydride, and thus adverselyaffect the rate of hydrogen generation. The distribution of the chemicalhydride particle size can be chosen to optimize for rate of reaction orfor hydrogen generation capacity. For example a monodispersedistribution of small chemical hydride particles would allow slow flowof water vapor through the chemical hydride, have a high hydrogengeneration capacity but a low rate of hydrogen generation. Amonodisperse large particle size distribution would allow faster flow ofwater vapor through the chemical hydride, have a high rate of hydrogengeneration, but have a low hydrogen generation capacity. A bimodaldistribution in which smaller particles of chemical hydride fit withinthe interstices of the larger chemical hydride particles could provide abalance between the rate of hydrogen generation and hydrogen generationcapacity. Other particle size distributions are also possible.

Additionally, by varying which chemical hydride is used, the rate ofreaction with water vapor can be adjusted, and therefore the rate ofhydrogen generation. This can also be accomplished by using mixtures oftwo or more chemical hydrides. By varying which chemical hydride isused, and at the same time using a mixture of chemical hydrides, andparticle size distribution, the rate of reaction of the chemical hydridewith water vapor can further be controlled.

The chemical hydride is described herein as a pellet. As used hereinthis term is used in a broad sense to describe any shape orconfiguration of the chemical hydride particles that occupy in the spaceallotted to the chemical hydride in the fuel source. Thus, the shape ofthe chemical hydride pellet is not critical. It may be a, layer, disk,tablet, sphere, or have no specific shape. The shape of the chemicalhydride particles may be determined by the shape of the fuel source andthe need to make the most efficient use of the space allotted to thechemical hydride. If appropriate, differently shaped chemical hydridepellets can be used within one fuel source.

The metal hydride pellet 106 functions as a sort of hydrogen sponge thatcan quickly adsorb or desorb hydrogen at an almost constant pressure. Apower generator with a fuel consisting of chemical hydride and metalhydride can accommodate pulses of power by using some of the hydrogenstored in the metal hydride, and can thus be designed for the averagepower of the range, resulting in lower cost, and reduced self-discharge.Additionally, sensitivity to ambient temperature and humidity may bereduced, because the power generator can draw on the hydrogen stored inthe metal hydride. Metal hydrides comprise ab5 compounds, ab2 compounds,ab compounds, complex alloys, intermetallic compounds, solid solutionalloys, or any combination thereof. Exemplary metal hydrides compriseLaNi₅, LaNi₄.6Mn_(0.4), MnNi_(3.5)Co_(0.7)Al_(0.8),MnNi₄.2Co_(0.2)Mn_(0.3)Al_(0.3), TiFe_(0.8)Ni_(0.2), CaNi₅,(V_(0.9)Ti_(0.1))_(0.95)Fe_(0.05), (V_(0.9)Ti_(0.1))_(0.95)Fe_(0.05),LaNi_(4.7)Al_(0.3), or any combination thereof.

The metal hydride is described herein as a pellet. As noted above, theterm metal hydride pellet used herein this term is used in a broad senseto describe any shape or configuration of the metal hydride thatoccupies the space allotted to the metal hydride in the fuel source.Thus, the shape in which the porous metal hydride exists is notcritical. It may be present as a porous film, web, layer, disk, tablet,sphere, or have no specific shape. The shape of the porous metal hydridepellet may be determined by the shape of the fuel source and the need tomake the most efficient use of the space allotted to the metal hydride.If appropriate, differently shaped metal hydride pellets can be usedwithin one fuel source.

Referring to FIG. 2, a cross-sectional view 200 of a fuel source isshown, according to some embodiments. In FIG. 2, the stack of two ormore chemical hydride pellets 204 may be separated by a metal hydridepellet 206. The metal hydride may act as both a gas diffusion channel,and as a reversible hydrogen storage element for rapid delivery ofhydrogen. The metal hydride 206 may be positioned such that two stacksof chemical hydride pellets 204 are formed. Two or more chemical hydridepellets 204 may be contacted with, or at least partially surrounded orwrapped with a flexible, porous water-vapor permeable layer 208 (such asTEFLON, GORE TEX, or NAFION). Each chemical hydride pellet 204 may beseparated by a spacer 214. Air gaps 202 are between individual chemicalhydride pellets 204, and between the chemical hydride pellets 204 andperforated enclosure 212. A liquid water impermeable, hydrogen andwater-vapor permeable membrane or a particulate membrane 210 (such asTEFLON, GORE TEX, or NAFION) may also be positioned between the pellets204 and enclosure 212. A particulate filter 214 may be positionedbetween the stacks of chemical hydride pellets 204 and enclosure 212.

In FIG. 3, an alternative cross-sectional view 300 of a fuel source isshown, according to some embodiments. Two or more compressed porouschemical hydride pellets 304 may be contacted with, or at leastpartially surrounded or wrapped with a flexible, porous, liquid waterimpermeable, hydrogen and water-vapor permeable layer 308 (such asTEFLON, GORE TEX, or NAFION) that prevents fuel particles from expandinginto the gas permeable porous layer 314 or into the region containingporous metal hydride 306. The gas permeable porous layer 314 can serveas a spacer between chemical hydride fuel pellets and between thechemical hydride fuel pellet and the metal fuel pellet. Porous metalhydride 306 is positioned adjacent one end of the stack of chemicalhydride pellets. Air gaps 302 are between individual pellets 304,perforated enclosure 312, and porous metal hydride 306. A liquid waterimpermeable, hydrogen and water-vapor permeable membrane or aparticulate membrane 310 (such as TEFLON, GORE TEX, or NAFION) may alsobe positioned between the pellets 304 and enclosure 312. The chemicalhydride pellets may be removable from the perforated enclosure andporous metal hydride. The chemical hydride pellets and a portion of theperforated enclosure may be removable from a portion of the enclosurecontaining the porous metal hydride.

The fuel source may be utilized in an electrochemical fuel system, suchas a system including one or more fuel cells configured to utilize thefuel generated from the fuel source. The fuel source may provide asource of hydrogen fuel for electrochemical cells to operate, such as inportable electronic devices.

The chemical hydride pellet stack may be a part of a removable anddisposable or recyclable cartridge for an electrochemical cell such as afuel cell. In such a cartridge, the metal hydride fuel would be retainedin the electrochemical cell, while the stack of chemical hydride pelletsand spacers would be removable. Alternatively, the chemical hydridepellets and a portion of the enclosure may be removable from theremainder of the enclosure containing the porous metal hydride. Thus, afresh chemical hydride pellet stack could replace an exhausted chemicalhydride pellet stack allowing the portion of the electrochemical cellcontaining the porous metal hydride to be reused. For example, thechemical hydride pellet stack can be the size of a standard AA, AAA, C,or D cell (or any other battery size) that can be removed and replaced.The exhausted chemical hydride pellet stack could also be recycled byaddition of new chemical hydride pellets.

1. A fuel source (100) for an electrochemical cell, comprising: two ormore chemical hydride pellets (104); a flexible, porous, liquid waterimpermeable, hydrogen and water vapor permeable membrane (108), incontact with and at least partially surrounding each chemical hydridepellet; and a porous metal hydride pellet (106), positioned between eachchemical hydride pellet.
 2. The fuel source of claim 1, furthercomprising: air gaps (102) between pellets; a perforated enclosure(112), substantially surrounding the chemical hydride pellets; and aliquid water impermeable, hydrogen and water vapor permeable membrane orparticulate filter (110) positioned between the chemical hydride pelletsand the enclosure.
 3. The fuel source of claim 1, wherein the chemicalhydride comprises LiAlH₄, NaAlH₄, KAlH₄, MgAlH₄, CaH₂, LiBH₄, NaBH₄,LiH, MgH₂, alkali metals, alkaline earth metals, alkali metal salicides,or any combinations thereof.
 4. The fuel source of claim 1, wherein thechemical hydride comprises LiAlH₄, NaAlH₄, NaBH₄, LiBH₄, LiH, or anycombination thereof.
 5. The fuel source of claim 1 wherein the metalhydride comprises ab5 compounds, ab2 compounds, ab compounds, complexalloys, intermetallic compounds, solid solution alloys, or anycombination thereof.
 6. The fuel source of claim 1 wherein the metalhydride comprises LaNi₅, LaNi₄.6Mn_(0.4), MnNi_(3.5)Co_(0.7)Al_(0.8),MnNi₄.2Co_(0.2)Mn_(0.3)Al_(0.3), TiFe_(0.8)Ni_(0.2), CaNi₅,(V_(0.9)Ti_(0.1))_(0.95)Fe_(0.05), (V_(0.9)Ti_(0.1))_(0.95)Fe_(0.05),LaNi_(4.7)Al_(0.3), or any combination thereof.
 7. A fuel source (200)for an electrochemical cell, comprising: two or more chemical hydridepellets (204), positioned in two or more stacks; a flexible, porous,liquid water impermeable, hydrogen and water vapor permeable membrane(208), in contact with and at least partially surrounding each chemicalhydride pellet; a porous metal hydride layer (206), separating eachchemical hydride pellet stack; and one or more spacers (214), positionedbetween each pellet.
 8. The fuel source of claim 7 further comprising:air gaps (202) between each pellet; a perforated enclosure (212),substantially surrounding the chemical hydride pellet stacks; and aflexible, porous, liquid water impermeable, hydrogen and water vaporpermeable membrane or particulate filter (210) positioned between thechemical hydride pellet stacks and the perforated enclosure.
 9. The fuelsource of claim 7, wherein the chemical hydride comprises LiAlH₄,NaAlH₄, KAlH₄, MgAlH₄, CaH₂, LiBH₄, NaBH₄, LiH, MgH₂, alkali metals,alkaline earth metals, alkali metal salicides, or any combinationthereof.
 10. The fuel source of claim 7, wherein the chemical hydridecomprises LiAlH₄, NaAlH₄, NaBH₄, LiBH₄, LiH, or any combination thereof.11. The fuel source of claim 7, wherein the metal hydrides comprise ab5compounds, ab2 compounds, ab compounds, complex alloys, intermetalliccompounds, solid solution alloys, or any combination thereof.
 12. Thefuel source of claim 7 wherein the metal hydrides comprise LaNi₅,LaNi₄.6Mn_(0.4), MnNi_(3.5)Co_(0.7)Al_(0.8),MnNi₄.2Co_(0.2)Mn_(0.3)Al_(0.3), TiFe_(0.8)Ni_(0.2), CaNi₅,(V_(0.9)Ti_(0.1))_(0.95)Fe_(0.05), (V_(0.9)Ti_(0.1))_(0.95)Fe_(0.05),LaNi_(4.7)Al_(0.3), or any combination thereof.
 13. A fuel source (300)for an electrochemical cell, comprising: two or more chemical hydridepellets (304), positioned in a stack; a flexible, porous, liquid waterimpermeable, hydrogen and water vapor permeable membrane (308), incontact with and at least partially surrounding each chemical hydridepellet; a liquid water impermeable, hydrogen and water vapor permeablemembrane or particulate filter (304) positioned between the pelletstacks and the perforated enclosure; one or more gas permeable layers orspacers (314), positioned between each chemical hydride pellet andbetween the chemical hydride pellet and the porous metal hydride layer;and a porous metal hydride layer (306), positioned adjacent to one endof the stack
 14. The fuel source of claim 13, further comprising: airgaps (302) between each pellet; a perforated enclosure (312),substantially surrounding the chemical hydride pellet stacks; andwherein the chemical hydride pellets are removable.
 15. The fuel sourceof claim 13, wherein the chemical hydride pellets are contained in aremovable cartridge.
 16. The fuel source of claim 13, wherein thechemical hydride comprises LiAlH₄, NaAlH₄, KAlH₄, MgAlH₄, CaH₂, LiBH₄,NaBH₄, LiH, MgH₂, alkali metals, alkaline earth metals, alkali metalsalicides, or any combination thereof.
 17. The fuel source of claim 13,wherein the chemical hydride comprises LiAlH₄, NaAlH₄, NaBH₄, LiBH₄,LiH, or any combination thereof.
 18. The fuel source of claim 13,wherein the metal hydrides comprise ab5 compounds, ab2 compounds, abcompounds, complex alloys, intermetallic compounds, solid solutionalloys, or any combination thereof.
 19. The fuel source of claim 13wherein the metal hydrides include LaNi₅, LaNi₄.6Mn_(0.4),MnNi_(3.5)Co_(0.7)Al_(0.8), MnNi₄.2Co_(0.2)Mn_(0.3)Al_(0.3),TiFe_(0.8)Ni_(0.2), CaNi₅, (V_(0.9)Ti_(0.1))_(0.95)Fe_(0.05),(V_(0.9)Ti_(0.1))_(0.95)Fe_(0.05), LaNi_(4.7)Al_(0.3), or anycombination thereof.